Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit cell) of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
In order for the middle or large-sized battery module to provide power and capacity required by a predetermined apparatus or device, it is necessary for the middle or large-sized battery module to be configured to have a structure in which a plurality of battery cells are electrically connected in series to each other, and the battery cells are stable against external force.
Also, the battery cells constituting the middle or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. If the heat, generated from the battery cells during the charge and discharge of the battery cells, is not effectively removed, the heat accumulates in the battery cells with the result that deterioration of the battery cells is accelerated. According to circumstances, the battery cells may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
Generally, a hybrid electric vehicle uses a power from a battery pack during starting of the hybrid electric vehicle and oil, such as gasoline, during traveling of the hybrid electric vehicle. As a result, an amount of heat generated from the battery pack is small, and therefore, a cooling system using air is generally used in a battery pack for vehicles, which is applied to the hybrid electric vehicle.
On the other hand, a plug-in hybrid electric vehicle uses a power from a battery pack for vehicles during early traveling of the plug-in hybrid electric vehicle as well as during starting of the plug-in hybrid electric vehicle. As a result, the size of the battery pack is increased, and the number of charging and discharging the battery pack is relatively increased. Consequently, an amount of heat generated from the battery pack is large.
Consequently, there is a high necessity for technology to fundamentally solve the above problems, thereby improving cooling efficiency of a battery module assembly included in a battery pack for vehicles.